Editing Interstellar travel (section)

=== Theoretical concepts ===

==== Transmission of minds with light ====
[[Mind uploading|Uploaded human minds]] or [[AI]] could be transmitted with laser or radio signals at the [[speed of light]].<ref>{{cite web |title=Michio Kaku foretells humanity's extraordinary future |website=[[NBC News]] |date=2 March 2018 |url=https://www.nbcnews.com/mach/science/michio-kaku-sees-amazing-things-our-future-except-those-scary-ncna851226 |quote=We're going to have the Human Connectome Project map the human brain before the end of this century, I think. We're going to put the connectome on a laser beam and shoot it to the moon. In one second, our consciousness is on the moon. In 20 minutes we're on Mars, eight hours we're on Pluto, in four years our consciousness has reached the nearest star. |access-date=20 December 2021 |archive-date=20 December 2021 |archive-url=https://web.archive.org/web/20211220134353/https://www.nbcnews.com/mach/science/michio-kaku-sees-amazing-things-our-future-except-those-scary-ncna851226 |url-status=live }}</ref> This requires a receiver at the destination which would first have to be set up e.g. by humans, probes, [[self replicating machines]] (potentially along with AI or uploaded humans), or an alien civilization (which might also be in a different galaxy, perhaps a [[Kardashev scale#Type_III|Kardashev type III civilization]]).

==== Artificial black hole ====

{{Main|Black hole starship}}
A theoretical idea for enabling interstellar travel is to propel a starship by creating an artificial black hole and using a parabolic reflector to reflect its [[Hawking radiation]]. Although beyond current technological capabilities, a black hole starship offers some advantages compared to other possible methods. Getting the black hole to act as a power source and engine also requires a way to convert the Hawking radiation into energy and thrust. One potential method involves placing the hole at the focal point of a parabolic reflector attached to the ship, creating forward thrust. A slightly easier, but less efficient method would involve simply absorbing all the gamma radiation heading towards the fore of the ship to push it onwards, and let the rest shoot out the back.<ref>{{cite arXiv | last1=Crane | first1=Louis | last2=Westmoreland | first2=Shawn | title=Are Black Hole Starships Possible | year=2009 | page=| class=gr-qc | eprint=0908.1803 }}</ref><ref>{{Cite journal |url=https://www.newscientist.com/article/mg20427361.000-dark-power-grand-designs-for-interstellar-travel.html |title=Dark power: Grand designs for interstellar travel |journal=New Scientist |date=25 November 2009 |issue=2736 |last=Chown |first=Marcus |access-date=1 September 2017 |archive-date=26 April 2015 |archive-url=https://web.archive.org/web/20150426175526/http://www.newscientist.com/article/mg20427361.000-dark-power-grand-designs-for-interstellar-travel.html |url-status=live }}{{subscription required}}</ref><ref>{{Cite news |url=http://io9.com/5391989/a-black-hole-engine-that-could-power-spaceships |title=A Black Hole Engine That Could Power Spaceships |first=Tim |last=Barribeau |date=November 4, 2009 |work=io9 |access-date=11 August 2016 |archive-date=22 November 2015 |archive-url=https://web.archive.org/web/20151122040407/http://io9.com/5391989/a-black-hole-engine-that-could-power-spaceships |url-status=live }}</ref>

==== Faster-than-light travel ====
[[File:Wormhole travel as envisioned by Les Bossinas for NASA.jpg|thumb|Artist's depiction of a hypothetical ''Wormhole Induction Propelled Spacecraft'', based loosely on the 1994 "[[Alcubierre drive|warp drive]]" paper of [[Miguel Alcubierre]]]]
{{Main|Faster-than-light}}

Scientists and authors have postulated a number of ways by which it might be possible to surpass the speed of light, but even the most serious-minded of these are highly speculative.<ref name="crawftl">{{cite journal|last1=Crawford|first1=Ian A.|title=Some thoughts on the implications of faster-than-light interstellar space travel|journal=Quarterly Journal of the Royal Astronomical Society|date=1995|volume=36|pages=205–218|bibcode=1995QJRAS..36..205C}}</ref>

It is also debatable whether faster-than-light travel is physically possible, in part because of [[Tachyonic antitelephone|causality]] concerns: travel faster than light may, under certain conditions, permit travel backwards in time within the context of [[special relativity]].<ref>{{cite journal|last1=Feinberg|first1=G.|title=Possibility of faster-than-light particles|journal=Physical Review|date=1967|volume=159|issue=5|pages=1089–1105|doi=10.1103/physrev.159.1089|bibcode = 1967PhRv..159.1089F }}</ref> Proposed mechanisms for [[faster-than-light]] travel within the theory of general relativity require the existence of [[exotic matter]]<ref name="crawftl" /> and, it is not known if it could be produced in sufficient quantities, if at all.

===== Alcubierre drive =====

{{Main|Alcubierre drive}}
In physics, the [[Alcubierre drive]] is based on an argument, within the framework of [[general relativity]] and without the introduction of [[wormhole]]s, that it is possible to modify spacetime in a way that allows a spaceship to travel with an arbitrarily large speed by a local expansion of spacetime behind the spaceship and an opposite contraction in front of it.<ref name="Warp Alcubierre">{{cite journal |title=The warp drive: hyper-fast travel within general relativity |journal=Classical and Quantum Gravity |year=1994 |last=Alcubierre |first=Miguel |volume=11 |issue=5 |doi=10.1088/0264-9381/11/5/001 |pages=L73–L77|arxiv = gr-qc/0009013 |bibcode = 1994CQGra..11L..73A |citeseerx=10.1.1.338.8690 |s2cid=4797900 }}</ref> Nevertheless, this concept would require the spaceship to incorporate a region of [[exotic matter]], or the hypothetical concept of [[negative mass]].<ref name="Warp Alcubierre" />

===== Wormholes =====
[[Wormhole]]s are conjectural distortions in spacetime that theorists postulate could connect two arbitrary points in the universe, across an [[Einstein–Rosen Bridge]]. It is not known whether wormholes are possible in practice. Although there are solutions to the Einstein equation of general relativity that allow for wormholes, all of the currently known solutions involve some assumption, for example the existence of [[negative mass]], which may be unphysical.<ref>{{cite web |url=http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html#worm |title=Ideas Based On What We'd Like To Achieve: Worm Hole transportation |date=11 March 2015 |publisher=NASA Glenn Research Center |access-date=4 September 2012 |archive-date=24 September 2013 |archive-url=https://web.archive.org/web/20130924060726/http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html#worm |url-status=live }}</ref> However, Cramer ''et al.'' argue that such wormholes might have been created in the early universe, stabilized by [[cosmic string]]s.<ref>{{cite journal | author= John G. Cramer| author2= Robert L. Forward| author3= Michael S. Morris| author4= Matt Visser| author5= Gregory Benford| author6= Geoffrey A. Landis | title= Natural Wormholes as Gravitational Lenses | journal= Physical Review D | volume= 51 | issue= 3117 | date= 15 March 1995 | pages= 3117–3120 | doi= 10.1103/PhysRevD.51.3117 | pmid= 10018782| arxiv= ph/9409051|bibcode = 1995PhRvD..51.3117C | s2cid= 42837620}}</ref> The general theory of wormholes is discussed by Visser in the book ''Lorentzian Wormholes''.<ref>{{cite book | author= Visser, M. | date= 1995 | title= Lorentzian Wormholes: from Einstein to Hawking | publisher= AIP Press, Woodbury NY | isbn= 978-1-56396-394-0}}</ref>